Project Summary MYC gene rearrangements in B cell non-Hodgkin lymphomas associate with aggressive disease and dismal outcomes, thus identifying a group of patients without therapeutic alternatives that represent an unmet medical need. Researchers have used mice to model MYC rearrangements in B cells but have failed to reproduce the spatial and temporal circumstances of their acquisition during lymphomagenesis. Access to refined, more accurate models would improve our understanding of the pathogenesis, biology, and genetics of these cancers and identify specific vulnerabilities amenable to therapeutic targeting. In this project, we propose to generate two novel and complementary mouse models of MYC-driven B cell non- Hodgkin lymphomas. A Myc/IgH gene rearrangement is targeted specifically to a subset of mature germinal center B cells ? the putative cells of origin of these malignancies. Alternatively, this rearrangement can be activated at specific timepoints during disease progression and reproduce late events associated with disease transformation, as observed in a fraction of Diffuse Large B cell and Follicular lymphomas. To address these points, we will: (1) Generate and validate a Cre-lox conditional ?-MYC mouse model for specific targeting of a Myc/Ig? translocation to B cell subsets. We have reengineered a ?-MYC transgene to render the Myc/Ig? translocation conditional to Cre-mediated recombination. Pronuclear injection of this construct in one-cell eggs will allow generation of a germinal center B cell-specific mouse strain (C?1-Cre background), which will be used in functional assays to confirm cell-specific activation of this rearrangement. (2) Generate and validate a cell-of-origin based, stochastic model of Burkitt lymphoma with genetic strategies originally developed for lineage tracing studies. This mouse model will be generated using embryonic stem cell targeting and CRISPR/Cas9 zygote editing technologies. In this model, stochastic Myc/IgH translocations will occur in affinity-selected B cells to better recreate the cellular origin of human Burkitt lymphoma. Accuracy of this model will be confirmed through in vivo functional studies using single-cell phenotypic and genetic analyses. With these new mouse models we will contribute: (i) unprecedented tools for the study of lymphoma initiation and progression; (ii) useful preclinical models of aggressive B cell lymphomas, for which there are little or no therapeutic options.